Cloutier, S., Wahl, K., Newberry, R. C. 2010. Playful handling mitigates the stressfulness of injections in laboratory rats. American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 721 (Abstract #P126).

Rats can be playfully handled (tickled) in a manner that mimics playful social contact with conspecifics. We hypothesized that the timing of tickling in relation to an intraperitoneal injection would affect the efficacy of tickling in reducing stress associated with the procedure. We assessed the effect of the timing of playful handling on 96 male Sprague–Dawley rats (Rattus norvegicus; Sim:(SD)fBR Albino; found free of internal/external parasites and disease via quarterly serology and parasitology, and yearly necropsy, evaluations). Rats were either injected with 1 mL/kg saline intraperitoneally (I) or handled similarly but not injected (control, C), and exposed to one of 2 handling treatments in the home cage: not handled (N) or tickled (T) for 2 min immediately before injection (B), after injection (A) or both before and after injection (BA), for a total of 8 treatment groups (IN, ITB, ITA, ITBA, CN, CTA, CTB, CTBA). Treatments were administered daily for 10 d starting at 32 d of age. We measured the duration of injection, and the rate of frequencymodulated 50-kHz ultrasonic vocalizations (FM-USVs) and audible vocalizations emitted during injection. Rats required a similar amount of time to inject whether they were tickled (ITB, ITA, ITBA) or not handled (IN). However, when injected, the tickled rats (ITB, ITA, ITBA) emitted more FM-USV (P < 0.0001), which are associated with positive affective states, than nonhandled rats (IN). Rats tickled both before and after injection (ITBA) emitted fewer audible calls (P < 0.0001), which are associated with aversive events, than the nonhandled rats (IN) when injected. These findings suggest that playful handling reduces stress associated with repeated injections, and that the beneficial effect of playful handling is strongest when provided briefly both immediately before and after injection.